Fall back to unpinned mcp when distribution metadata is missing

Also pin down two test contracts on the new requirement helper: the
dev-version fallback preserves extras, and a user-supplied mcp[cli]
coexists with the pinned requirement rather than deduplicating into it.

Author: maxisbey

src/mcp/cli/claude.py

@@ -20,9 +20,13 @@ def mcp_requirement(package: str = "mcp") -> str:
     an unpinned `mcp` means the latest stable release — not necessarily the
     version the user installed (pre-releases in particular are never selected
     without an explicit pin). Source builds carry dev/local version segments
-    that are not published to PyPI, so they fall back to the unpinned form.
+    that are not published to PyPI, so they fall back to the unpinned form,
+    as does a missing distribution (no metadata to pin from).
     """
-    version = importlib.metadata.version("mcp")
+    try:
+        version = importlib.metadata.version("mcp")
+    except importlib.metadata.PackageNotFoundError:
+        return package
     if ".dev" in version or "+" in version:
         return package
     return f"{package}=={version}"

tests/cli/test_claude.py

@@ -43,6 +43,7 @@ def test_mcp_requirement_leaves_dev_versions_unpinned(monkeypatch: pytest.Monkey
     """Dev versions are not published to PyPI, so the requirement falls back to the unpinned package."""
     _set_mcp_version(monkeypatch, "2.0.0a2.dev3")
     assert mcp_requirement() == "mcp"
+    assert mcp_requirement("mcp[cli]") == "mcp[cli]"
 
 
 def test_mcp_requirement_leaves_local_versions_unpinned(monkeypatch: pytest.MonkeyPatch):
@@ -51,6 +52,17 @@ def test_mcp_requirement_leaves_local_versions_unpinned(monkeypatch: pytest.Monk
     assert mcp_requirement() == "mcp"
 
 
+def test_mcp_requirement_falls_back_when_mcp_is_not_installed(monkeypatch: pytest.MonkeyPatch):
+    """Without distribution metadata there is no version to pin, so the requirement stays unpinned."""
+
+    def raise_not_found(distribution_name: str) -> str:
+        raise importlib.metadata.PackageNotFoundError(distribution_name)
+
+    monkeypatch.setattr(importlib.metadata, "version", raise_not_found)
+    assert mcp_requirement() == "mcp"
+    assert mcp_requirement("mcp[cli]") == "mcp[cli]"
+
+
 def _read_server(config_dir: Path, name: str) -> dict[str, Any]:
     config = json.loads((config_dir / "claude_desktop_config.json").read_text())
     return config["mcpServers"][name]
@@ -75,13 +87,21 @@ def test_file_spec_without_object_suffix(config_dir: Path):
 
 
 def test_with_packages_sorted_and_deduplicated(config_dir: Path):
-    """Extra packages should appear as --with flags, sorted and deduplicated with mcp[cli]."""
+    """Extra packages should appear as sorted --with flags with duplicates removed."""
     assert update_claude_config(file_spec="s.py:app", server_name="s", with_packages=["zebra", "aardvark", "zebra"])
 
     args = _read_server(config_dir, "s")["args"]
     assert args[:8] == ["run", "--frozen", "--with", "aardvark", "--with", "mcp[cli]==1.2.3", "--with", "zebra"]
 
 
+def test_explicit_mcp_cli_kept_alongside_pinned_requirement(config_dir: Path):
+    """A user-supplied mcp[cli] no longer collapses into the pinned requirement; uv resolves both to the pin."""
+    assert update_claude_config(file_spec="s.py:app", server_name="s", with_packages=["mcp[cli]"])
+
+    args = _read_server(config_dir, "s")["args"]
+    assert args[:6] == ["run", "--frozen", "--with", "mcp[cli]", "--with", "mcp[cli]==1.2.3"]
+
+
 def test_with_editable_adds_flag(config_dir: Path, tmp_path: Path):
     """with_editable should add --with-editable after the --with flags."""
     editable = tmp_path / "project"